DOCSIS standard permits the addition of high-speed data transfer to an existing cable TV (CATV) system. Many cable television operators apply DOCSIS to provide internet access over their existing hybrid fiber-coaxial (HFC) network infrastructure.
A cable modem (CM) is a type of network device that provides bi-directional data communication via radio frequency channels on the HFC network. The cable modem will work with a cable modem terminal system (CMTS) in the network, which is a headend device of the cable television operator used to forward digital IP packets to and from the cable modem to provide high speed data services to cable subscribers.
Conventionally a cable modem of DOCSIS based network can only work with one CMTS at a certain time. The cable modem will firstly search for the available downstream and upstream channels broadcasted by the CMTS at initialization. After channel locked, the cable modem will complete a ranging phase and an IP initialization phase, then reach agreement with the CMTS on the channel bonding set and service flow contracts. From then on, the cable modem works as layer 2 bridge to forward packets between the cable interface and CPE interface.
FIG. 1 is an exemplary diagram showing a conventional network architecture for DVB live TV distribution. As shown in FIG. 1, a CMTS exchanges IP packets with an IP backbone network over Ethernet cable 101. Downstream RF (Radio Frequency) signals 102 from the CMTS of IP backbone network and a DVB service platform are mixed by a RF mixer. It can be appreciated that the RF mixer is a passive component for mixing the RF signals from various incoming paths to one outgoing path. The mixed RF signal is transmitted to a fiber node over HFC fiber 103, which will exchanges signals with a cable modem over RF cable 104. The fiber node also transmits feedback signals to the CMTS over a HFC fiber 103. The cable modem can exchange data packets with one or more CPEs (Customer Premise Equipments). For example, as shown in FIG. 1, the cable modem can provide bi-directional communications with a PC over Ethernet cable 101 or with a STB (Set-Top-Box) over Ethernet cable 101 or RF cable 104. Feedback signal from the cable modem over cable is converted to a fiber signal at the fiber node and transmitted to the CMTS headend directly over a return path 105. So the bi-directional data communication between CMTS and cable modem actually is splitted into different paths for downstream and upstream respectively.
Currently many chips used in cable modems have full band capability to tune to multiple RF channels at the same time. However, such band capability was not fully used.